Optical information recording medium

ABSTRACT

The present invention provides an optical information recording medium comprising a substrate including a groove that has a track pitch of 200 to 400 nm and a depth of 20 to 150 nm, the substrate having successively disposed thereon a light-reflective layer, a recording layer containing a dye and on which information is recordable by a laser beam having a wavelength of 600 nm or less, and a cover layer, wherein the recording layer contains at least two organic solvent-soluble compounds each having an absorption maximum in the range of 300 to 450 nm and a specific absorbance at a recording laser wavelength.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical information recordingmedium, and more specifically to an optical information recording mediumwritable only once by heat mode.

[0003] 2. Description of the Related Art

[0004] A CD-R is a writable, optical information recording medium(optical disc) on which information can be written only once byirradiation with laser light, and is widely known. A CD-R typicallycomprises a transparent disc substrate having successively disposedthereon a recording layer including an organic dye, a light-reflectivelayer including a metal such as gold, and a protective layer (coverlayer) made of a resin. Information is recorded on this CD-R byirradiating the CD-R with near-infrared laser light (usually laser lighthaving a wavelength of around 780 nm). Specifically, the portion of therecording layer that is irradiated absorbs light, whereby thetemperature rises at the irradiated portion. The rise in temperatureproduces a physical or chemical change (e.g., formation of pits) toalter the optical properties of the irradiated portion, wherebyinformation is recorded. The information thus recorded on the CD-R isordinarily reproduced by irradiating the CD-R with laser light havingthe same wavelength as that of the laser light used to record theinformation and detecting a difference in reflectance between the regionof the recording layer whose optical properties have been changed(recorded portion) and the region of the recording layer whose opticalproperties have not been changed (unrecorded portion).

[0005] In recent years, there has been a demand for optical informationrecording media having higher density, and writable digital versatilediscs (DVD-Rs) have been proposed in response to that demand (Nikkei NewMedia, extra issue entitled “DVD”, 1995). A DVD-R typically comprisestwo transparent disc substrates that each have successively disposedthereon a recording layer containing an organic dye, a light-reflectivelayer, and a protective layer, with the discs being adhered so that therecording layers face inward or so that protective substrates having thesame disc shape as these discs are disposed on outer sides of theadhered discs. Moreover, the transparent disc substrate includes a guidegroove (pre-groove) used for tracking a laser irradiated onto the CD-R,with the groove having a narrow track pitch (0.74 to 0.8 μm) that isequal to or less than half of that in a CD-R. Information is recordedand reproduced (played back) by irradiating the DVD-R with laser lightin a visible region (usually laser light having a wavelength regionranging from 630 to 680 nm), whereby information can be recorded at ahigher density than a CD-R.

[0006] Recently, high-vision television and networks such as theInternet have rapidly become more widespread. In addition, the start ofHDVT (High Definition Television) broadcasting is near at hand. As aresult, large-capacity optical recording media capable of recordingvisual information easily and inexpensively are in demand. While DVD-Rscurrently play a significant role as large-capacity recording media, thedemand for media having greater recording capacity and higher densitycontinues to escalate, and development of recording media that can copewith this demand is also needed. For this reason, development ofrecording media having ever greater storage capacity with whichhigh-density recording can be effected with short wave light continuesto advance.

[0007] Methods for recording information on and reproducing informationfrom an optical information recording medium including a recording layercontaining an organic dye, by irradiating, from the side of the mediumdisposed with the recording layer towards the side of the mediumdisposed with a light-reflecting layer, the medium with laser lighthaving a wavelength of 530 nm or less, are disclosed in, for example,Japanese Patent Application Laid-Open (JP-A) Nos. 4-74690, 7-304256,7-304257, 8-127174, 11-53758, 11-334204, 11-334205, 11-334206,11-334207, 2000-43423, 2000-108513, 2000-113504, 2000-149320,2000-158818 and 2000-228028. In these methods, information is recordedon and reproduced from an optical disc having a recording layercontaining a porphyrin compound, an azo-based dye, a metal azo-baseddye, a quinophthalone-based dye, a trimethine cyanine dye, adicyanobiphenyl-skeleton dye, a coumarin dye, a naphthalocyaninecompound or the like, by irradiating the optical disc with a blue laser(having a wavelength of 430 nm or 488 nm) or a blue-green laser (havinga wavelength of 515).

[0008] Further, in view of compatibility with CD-R systems currentlyemployed, optical information recording media have been proposed inwhich information can be recorded and reproduced by two laser beamshaving mutually different wavelengths. For example, in JP-A Nos.2000-141900, 2000-158816, 2000-185471, 2000-289342 and 2000-309165,there are proposed optical information recording media with whichinformation can be recorded and reproduced using both a laser beamhaving a wavelength at about 780 nm in a near-infrared region and alaser beam having a wavelength at about 650 nm in a visible region, bycombined use of a dye used in CD-Rs and a dye used in DVD-Rs.

[0009] However, the present inventors have found that practicallyemployable sensitivity cannot be obtained with the discs disclosed inthe above publications when information is recorded on the discs byirradiating the discs with short-wave laser beam having a wavelength of600 nm or less, and particularly a wavelength of 450 nm or less, andthat sufficient levels cannot been achieved with respect to otherrecording characteristics such as reflectance and modulation. Inparticular, it was found that recording characteristics of the opticaldiscs disclosed in the above publications decreased when the discs wereirradiated with laser light having a wavelength of 450 nm or less.

SUMMARY OF THE INVENTION

[0010] In view of the foregoing, it is an object of the presentinvention to provide an optical information recording medium on whichinformation can be recorded by irradiating the medium with a short-wavelaser beam having a wavelength of 600 nm or less, and that exhibitsstable playback characteristics.

[0011] The object is achieved by the invention described below.

[0012] A first aspect of the invention provides an optical informationrecording medium comprising a substrate including a groove that has atrack pitch of 200 to 400 nm and a depth of 20 to 150 nm, the substratehaving successively disposed thereon a light-reflective layer, arecording layer containing a dye and on which information is recordableby a laser beam having a wavelength of 600 nm or less, and a coverlayer, wherein the recording layer contains at least one organicsolvent-soluble compound having an absorption maximum in the range of300 to 450 nm and an absorbance of 0.07 or more at a recording laserwavelength, and at least one organic solvent-soluble compound having anabsorption maximum in the range of 300 to 450 nm and an absorbance oflower than 0.07 at a recording laser wavelength.

[0013] A second aspect of the invention provides an optical informationrecording medium comprising a substrate including a groove that has atrack pitch of 200 to 400 nm and a depth of 20 to 150 nm, the substratehaving successively disposed thereon a light-reflective layer, arecording layer containing a dye and on which information is recordableby a laser beam having a wavelength of 600 nm or less, and a coverlayer, wherein the recording layer contains at least two organicsolvent-soluble compounds, each having an absorption maximum in therange of 300 to 450 nm and an absorbance of 0.07 or more at a recordinglaser wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a graph illustrating absorption spectrums of aphthalocyanine compound (ORASOL BLUE GN, manufactured by Chiba SpecialtyChemical Corp.) and an anthracene compound (ORASOL BLUE BL, manufacturedby Chiba Specialty Chemical Corp.).

[0015]FIG. 2 is a graph illustrating an absorption spectrum of FOM-561manufactured by Wako Pure Chemical Industries, Ltd.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] An optical information recording medium of the present inventioncomprises a substrate having successively disposed thereon at least alight-reflective layer, a recording layer, and a cover layer. It ispreferable that the cover layer is formed via a bonding layer on therecording layer.

[0017] Substrate

[0018] Materials conventionally used for optical information recordingmedia substrates can be arbitrarily selected and used as the materialfor the substrate of the invention.

[0019] Specific examples of such substrate materials include glass,polycarbonate, acrylic resins such as polymethyl methacrylate, vinylchloride resins such as polyvinyl chloride and copolymers of vinylchloride, epoxy resins, amorphous polyolefins, polyesters, and metalssuch as aluminum. If necessary, these materials may be used incombination.

[0020] Among the materials listed above, polycarbonate and amorphouspolyolefins are preferable from the standpoint of moisture resistance,dimension stability, and low cost. Polycarbonate is particularlypreferable. The thickness of the substrate is preferably 1.1±0.3 mm.

[0021] A guide groove for tracking or a pre-groove representinginformation such as address signals is formed on the substrate. In orderto achieve higher storage density, it is preferable to use a substratehaving a pre-groove with a track pitch that is narrower than the trackpitch in a conventional CD-R or DVD-R. It is essential that the trackpitch of the pre-groove is 200 to 400 nm. Preferably, the track pitch ofthe pre-groove is 250 to 350 nm. It is also essential that the depth ofthe pre-groove is 20 to 150 nm. Preferably, the depth of the pre-grooveis 50 to 100 nm.

[0022] An undercoat layer is preferably disposed on the surface of thesubstrate at the side disposed with the light-reflective layer, in orderto improve surface smoothness and enhance adhesion.

[0023] Examples of material for the undercoat layer include polymericsubstances such as polymethyl methacrylate, acrylic acid/methacrylicacid copolymers, styrene/maleic anhydride copolymers, polyvinyl alcohol,N-methylolacrylamide, styrene/vinyltoluene copolymers, chlorosulfonatedpolyethylene, nitrocellulose, polyvinyl chloride, chlorinatedpolyolefin, polyester, polyimide, vinyl acetate/vinyl chloridecopolymers, ethylene/vinyl acetate copolymers, polyethylene,polypropylene, polycarbonate, and the like; and surface-modifying agentssuch as silane coupling agents.

[0024] The undercoat layer can be formed by preparing a coating liquidby dissolving or dispersing the above-mentioned material in a suitablesolvent, and applying the coating liquid to the substrate surface byspin coating, dip coating, extrusion coating, or the like. The thicknessof the undercoat layer is normally 0.005 to 20 μm and preferably 0.01 to10 μm.

[0025] Light-reflective Layer

[0026] A material having a high reflectance with respect to lasers isused for the light-reflective layer. It is preferable that thereflectance is 70% or more.

[0027] Examples of the light-reflective material include metals andsemimetals such as Mg, Se, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re,Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Si, Ge,Te, Pb, Po, Sn, and Bi, and stainless steel. These light-reflectivematerials may be used singly or in combination of two or more, oralternatively as alloys. Among these materials, Cr, Ni, Pt, Cu, Ag, Au,Al, and stainless steel are preferable. Au, Ag, Al, and their alloys aremore preferable. Au, Ag, and their alloys are most preferable.

[0028] The light-reflective layer can be formed by, for example,vacuum-depositing, sputtering, or ion-plating the light-reflectivematerial on the substrate. The thickness of the light-reflective layeris normally 10 to 300 nm and preferably 50 to 200 nm.

[0029] Recording Layer

[0030] The recording layer is formed on the light-reflective layer andcontains a dye. Information can be recorded on the recording layer whenthe recording layer is irradiated with a laser having a wavelength of600 nm or less.

[0031] In the first aspect of the invention, examples of the dye includea combination of at least one organic solvent-soluble compound that hasan absorption maximum in the range of 300 to 450 nm and an absorbance of0.07 or more at the recording laser wavelength (hereinafter, “theorganic solvent-soluble compound (A)”) and at least one organicsolvent-soluble compound that has an absorption maximum in the range of300 to 450 nm and an absorbance of lower than 0.07 at the recordinglaser wavelength (hereinafter, “the organic solvent-soluble compound(B)”).

[0032] The term “absorption maximum” refers not only to cases where theabsorption exhibits a maximum in the range of 300 to 450 nm but alsocases where the absorbance becomes 0.2 or more.

[0033] By mixing the organic solvent-soluble compounds (A) and (B),which have mutually different absorbances at a recording laserwavelength, at a desired mixing ratio, a mixture of compounds havingdifferent thermal absorption properties is produced. As a result, thedispersion behavior of the recording layer can be made different fromthat of a recording layer comprising only a single compound, whereby itbecomes possible to successfully control pit formation and raise thedegree of modulation.

[0034] The term “recording laser wavelength” refers to the generallydefined wavelength of a laser that is irradiated on an opticalinformation recording medium to cause decomposition of the components ofthe recording layer (dye layer). The actual wavelength may deviate fromthe generally defined wavelength by ±10 nm. For example, the wavelengthis 635 nm or 650 nm in the case of a DVD and 405 nm in the case of a DVR(a high-density storage medium of 22.5 GB/disc proposed by Sony Corp.).

[0035] The term “absorbance” refers to the absorbance obtained byforming a solid film (having a thickness of, for example, 100 nm) of theorganic solvent-soluble compound (A) or (B) on a flat substrate ofpolycarbonate and measuring the transmittance by means of aspectrophotometer (uv-3100, manufactured by Shimadzu Corporation).

[0036] The mixing ratio by mass of the organic solvent-soluble compounds(A) and (B) (i.e., (A)/(B)) is preferably 5/95 to 95/5 and morepreferably 10/90 to 90/10.

[0037] If the mixing ratio is less than 5/95 or more than 95/5, theeffect of using the mixture to control thermal properties becomesinsignificant and may not be much different from the case where a singlecompound is used.

[0038] The amount of the organic solvent-soluble compound (A) includedin the recording layer is preferably 5 to 95% by mass and morepreferably 10 to 90% by mass.

[0039] A sufficient effect may not be exhibited if the amount is lessthan 5% by mass, and further effects may not be exhibited even if thecontent exceeds 95% by mass.

[0040] The organic solvent-soluble compound (A) is a phthalocyaninecompound or a porphyrin compound, and is preferably at least one ofthese compounds. The phthalocyanine compound is preferably at least oneof a sulfamoyl-substituted phthalocyanine compound, an alkyl-substitutedphthalocyanine compound, and an alkoxy-substituted phthalocyaninecompound.

[0041] The organic solvent-soluble compound (B) is phthalocyanine,anthracene, or a derivative of these compounds, and is preferably atleast one of these compounds. The phthalocyanine compound is preferablyat least one of a sulfamoyl-substituted phthalocyanine compound, analkyl-substituted phthalocyanine compound, and an alkoxy-substitutedphthalocyanine compound.

[0042] Examples of the anthracene compound that can be used includeanthracene, a sulfamoyl-substituted anthracene compound, analkyl-substituted anthracene compound, and an alkoxy-substitutedanthracene compound.

[0043]FIG. 1 shows specific examples of the absorption spectrum of aphthalocyanine compound (ORASOL BLUE GN, manufactured by Chiba SpecialtyChemical Corp.) used as the organic solvent-soluble compound (A), andthe absorption spectrum of an anthracene compound (ORASOL BLUE BL,manufactured by Chiba Specialty Chemical Corp.) used as the organicsolvent-soluble compound (B).

[0044] As shown in FIG. 1, the absorbances of (A) and (B) at therecording laser wavelength (405 nm) of a DVR are 0.07 and 0.06,respectively.

[0045] The effect described above is obtained by using a combination ofthe organic solvent-soluble compounds (A) and (B).

[0046] In the second aspect of the invention, the dye at least containstwo or more organic solvent-soluble compounds, with each having anabsorption maximum in the range of 300 to 450 nm and an absorbance of0.07 or more at the recording laser wavelength.

[0047] If two or more organic solvent-soluble compounds whoseabsorbances at the recording laser wavelength are each 0.07 or more areincorporated, the amount of light absorption can be controlled and ahigh degree of modulation can be brought about.

[0048] The term “absorbance” as used herein refers to an amountindicating the proportion of light absorbed by the organicsolvent-soluble compound in an amorphous state. More specifically, thevalue is log₁₀(I₀/I), where I₀, is light intensity before absorption andI is light intensity changed by absorption.

[0049] More specifically, the absorbance is obtained by the forming asolid film (having a thickness of, for example, 100 nm) of the organicsolvent-soluble compound on a flat substrate of polycarbonate andmeasuring the transmittance by means of a spectrophotometer (uv-3100,manufactured by Shimadzu Corporation).

[0050] When the number of organic solvent-soluble compounds whoseabsorbances at the recording laser wavelength are each 0.07 or more is 2and these organic solvent-soluble compounds are designated as X and Y,the mixing ratio by mass of the organic solvent-soluble compounds (i.e.,X/Y) is preferably 0.1/99.9 to 99.9/0.1 and more preferably 1/99 to99/1.

[0051] The properties of the intended compound may not be exhibitedeffectively if the mixing ratio is less than 0.1/99.9, and theproperties of the compound may predominate if the mixing ratio exceeds99.9/0.1.

[0052] When the number of organic solvent-soluble compounds whoseabsorbances at the recording laser wavelength are each 0.07 or more is 3or more, the mixing ratio by mass of the organic solvent-solublecompound X, whose content (amount) in the recording layer is thelargest, to the organic solvent-soluble compound Y, whose content in therecording layer is the smallest, must meet the above-mentioned mixingratio by mass.

[0053] The amount of the two or more organic solvent-soluble compoundsincluded in the recording layer is preferably 50 to 100% by mass andmore preferably 70 to 100% by mass.

[0054] If the content is 50% by mass or less, absorption diminishes andthere may be a drop in recording characteristics.

[0055] The organic solvent-soluble compounds in the second aspect arepreferably a phthalocyanine compound, a porphyrin compound, a triazolecompound, an aminobutadiene compound, and a cyanine compound. Thephthalocyanine compound to be used is preferably one of analkoxy-substituted phthalocyanine compound, a sulfonamide-substitutedphthalocyanine compound, a sulfamoyl-substituted phthalocyaninecompound, and a sulfonic acid-substituted phthalocyanine compound.

[0056]FIG. 2 shows the absorption spectrum of FOM-561, which is aspecific example of the organic solvent-soluble compound and is aphthalocyanine compound manufactured by Wako Pure Chemical Industries,Ltd.

[0057] As shown in FIG. 2, the absorbance at the recording laserwavelength (405 nm) of a DVR is 0.1146.

[0058] The effect described above is obtained by using two or more suchorganic solvent-soluble compounds.

[0059] In addition, the dyes described in JP-A Nos. 4-74690, 8-127174,11-53758, 11-334204, 11-334205, 11-334206, 11-334207, 2000-43423,2000-108513, and 2000-158818 can also be used in combination with theabove-mentioned organic solvent-soluble compounds.

[0060] Other examples of the dye include organic compounds, such astriazole compounds, triazine compounds, cyanine compounds, merocyaninecompounds, aminobutadiene compounds, phthalocyanine compounds, cinnamicacid compounds, viologen compounds, azo compounds, oxonolbenzoxazolecompounds, and benzotriazole compounds. Among these compounds, cyaninecompounds, aminobutadiene compounds, benzotriazole compounds, andphthalocyanine compounds are particularly preferable.

[0061] The recording layer is formed by preparing a dye coating liquidby dissolving the recording material (organic solvent-soluble compoundor the like), such as the above-mentioned dye, a binder, and otheradditives as needed, in a suitable solvent, applying the dye coatingliquid to the light-reflective layer formed on the substrate surface,and drying the layer. The concentration of the recording material in thedye coating liquid is generally 0.01 to 15% by mass, preferably 0.1 to10% by mass, more preferably 0.5 to 5% by mass, and most preferably 0.5to 3% by mass.

[0062] The recording material may be dissolved by, for example, heat,ultrasonic treatment, or stirring the material with a stirrer,disperser, or homogenizer.

[0063] Examples of the solvent for preparing the dye coating liquidinclude esters such as butyl acetate, ethyl lactate, and cellosolveacetate; ketones such as methyl ethyl ketone, cyclohexanone, and methylisobutyl ketone; chlorinated hydrocarbons such as dichloromethane,1,2-dichloroethane, and chloroform; amides such as dimethylformamide;hydrocarbons such as methylcyclohexane; ethers such as tetrahydrofuran,ethyl ether, and dioxane; alcohols such as ethanol, n-propanol,isopropanol, n-butanol, and diacetone alcohol; fluorine-based solventssuch as 2,2,3,3-tetrafluoropropanol; and glycol ethers such as ethyleneglycol monomethyl ether, ethylene glycol monoethyl ether, and propyleneglycol monomethyl ether.

[0064] These solvents may be used singly or in combination of two ormore by taking into consideration the solubility of the recordingmaterial to be used. The dye coating liquid may also contain additivessuch as an antioxidant, a UV absorber, a plasticizer, and a lubricatingagent.

[0065] If a binder is used, examples of the binder include naturallyoccurring organic polymeric substances such as gelatin, cellulosederivatives, dextran, rosin, and rubber; and synthetic organic polymers,for example, hydrocarbon-based resins such as polyethylene,polypropylene, polystyrene, and polyisobutylene; vinyl-based resins suchas polyvinyl chloride, polyvinylidene chloride, and vinyl chloride/vinylacetate copolymers; acrylic resins such as polymethyl acrylate andpolymethyl methacrylate; polyvinyl alcohol, chlorinated polyethylene,epoxy resins, butyral resins, rubber derivatives, and pre-condensates ofheat-curable resins, e.g., phenol/formaldehyde resins. If the binder isused as a material for the recording layer, the amount of the binder isgenerally 0.01 to 50 times (by mass ratio), and preferably 0.1 to 5times (by mass ratio), relative to the recording material. Theconcentration of the recording material in the coating liquid thusprepared is normally 0.01 to 10% by mass and preferably 0.1 to 5% bymass.

[0066] The dye solution may be coated by spraying, spin coating, dipcoating, roll coating, blade coating, doctor roll coating, or screenprinting. The recording layer may comprise a single layer or severallayers. The thickness of the recording layer is normally 20 to 500 nm,preferably 30 to 300 nm, and more preferably 50 to 100 nm.

[0067] In order to raise the lightfastness of the recording layer,various kinds of anti-fading agents may be incorporated in the recordinglayer.

[0068] Generally, a singlet oxygen quencher is used as the anti-fadingagent. Singlet oxygen quenchers already described in publications suchas patent specifications can be used.

[0069] Specific examples of the singlet oxygen quencher include thosedescribed in JP-A Nos. 58-175693, 59-81194, 60-18387, 60-19586,60-19587, 60-35054, 60-36190, 60-36191, 60-44554, 60-44555, 60-44389,60-44390, 60-54892, 60-47069, 63-209995, and 4-25492, Japanese PatentApplication Publication (JP-B) Nos. 1-38680 and 6-26028, German PatentNo. 350399, and Journal of the Chemical Society of Japan, Oct,. 1992, p.1141.

[0070] The amount of the singlet oxygen quencher is normally 0.1 to 50%by mass, preferably 0.5 to 45% by mass, more preferably 3 to 40% bymass, and particularly preferably 5 to 25% by mass relative to theamounts of the compounds constituting the recording layer.

[0071] Bonding Layer

[0072] The bonding layer is an optional layer formed in order to raiseadhesion between the recording layer and the cover layer.

[0073] A photo-curable resin is preferable as the material constitutingthe bonding layer. In particular, a photo-curable resin having a smallercoefficient of contraction by hardening is preferable in order toprevent warping of the disc. Examples of these photo-curable resinsinclude UV-curable resins (UV-curable adhesives) such as “SD-640” and“SD-347” manufactured by Dainippon Ink & Chemicals, Inc. In order forthe bonding layer to have elasticity, the thickness of the bonding layeris preferably 1 to 1000 μm, more preferably 5 to 500 μm, andparticularly preferably 10 to 100 μm.

[0074] Cover Layer

[0075] The cover layer is formed in order to prevent water frompenetrating into the interior of the optical information recordingmedium. The material of the cover layer is not particularly limited aslong as it is transparent. The cover layer preferably comprisespolycarbonate, cellulose triacetate, or the like. More preferably, thematerial of the cover layer is a material whose coefficient of moistureabsorption under the conditions of 50% RH and 23° C. is 5% or less.

[0076] The term “transparent” means that the material is transparentenough to allow light for recording and playback to pass through thematerial (transmittance: 90% or more).

[0077] The cover layer is formed by preparing a coating solution bydissolving a photo-curable resin for forming the bonding layer in asuitable solvent, applying the coating liquid to the recording layer ata predetermined temperature to form a coated layer, laminating acellulose triacetate film (TAC film), which is obtained by, for example,extrusion of plastic, to the coated layer, and irradiating the resultinglaminate with light from the laminated TAC film side to thereby cure thecoating layer. It is preferable that the TAC film contains anultraviolet absorbing agent. The thickness of the cover layer is 0.01 to0.2 mm, preferably 0.03 to 0.1 mm, and more preferably 0.05 to 0.095 mm.

[0078] In order to control viscosity, the temperature at which coatingis conducted is preferably 23 to 50° C., more preferably 24 to 40° C.,and most preferably 25 to 37° C.

[0079] In order to prevent the disc from warping, it is preferable thata pulse-type light irradiator (preferably a UV irradiator) is used toirradiate the coating layer with ultraviolet light. The pulse intervalis preferably msec or less and more preferably μsec or less. Althoughthe amount of light irradiated per pulse is not particularly limited, itis preferably 3 kW/cm² or less and more preferably 2 kW/cm² or less.

[0080] Although the number of irradiation times is not particularlylimited, it is preferably 20 or less and more preferably 10 or less.

[0081] In the optical information recording medium of the invention,depending on the characteristics of the recording layer, a dielectriclayer or a light-transmissive layer may be formed between thelight-reflective layer and the recording layer. For example, if arecording layer containing the organic solvent-soluble compounds (A) and(B) is used, a light-transmissive layer may be disposed in order toimprove adhesion to the recording layer; and if a phase transitionrecording layer is used, a dielectric layer may be disposed in order todissipate heat.

[0082] The dielectric layer is made of a material such as an oxide, anitride, a carbide, a sulfide, etc. comprising at least one of Zn, Si,Ti, Te, Sm, Mo, and Ge, and the material may be hybridized (e.g.,ZnS-SiO₂).

[0083] Any material may be used for the light-transmissive layer as longas it has a transmittance of 90% or more at a laser wavelength. Forexample, the same material as that for the dielectric layer may be used.

[0084] The dielectric layer or the light-transmissive layer can beformed according to a conventionally known method. The thickness of thedielectric layer is preferably 1 to 100 nm and the thickness of thelight-transmissive layer is preferably 1 to 100 nm.

EXAMPLES

[0085] The present invention is explained in more detail by way ofexamples given below. It should be noted that the invention is notlimited to the following examples.

[0086] Mode 1

Examples 1 to 9

[0087] Grooved sides of spirally grooved polycarbonate substrates, whichwere obtained by injection molding and which each had a thickness of 1.2mm and a diameter of 120 mm and had groove depth, track pitch, and widthaccording to Table 1 (polycarbonate manufactured by Teijin Ltd., tradename: PANLITE AD5503), were sputtered with Ag so that a reflective layerhaving a thickness of 100 nm was formed. Next, 20 g of a mixture, whichwas composed of 95% by mass of ORASOL BLUE GN (phthalocyanine having anabsorbance of 0.07, manufactured by Chiba Specialty Chemical Corp.) and5% by mass of ORASOL BLUE BL (anthracene having an absorbance of 0.06,manufactured by Chiba Specialty Chemical Corp.) was dissolved in 1 L of2,2,3,3-tetrafluoropropanol by carrying out an ultrasonic treatment for2 hours to thereby obtain a dye coating liquid.

[0088] When the absorbances of ORASOL BLUE GN and ORASOL BLUE BL weremeasured, the absorption wavelengths shown in FIG. 1 were obtained.

[0089] The absorbance of ORASOL BLUE GN was obtained by forming a solidfilm thereof (having a thickness of 100 nm) on a flat substrate ofpolycarbonate and measuring the absorbance by the apparatus andcondition given below. The absorbance of ORASOL BLUE BN was measured ina similar way.

[0090] Measuring apparatus: spectrophotometer (uv-3100-PC manufacturedby Shimadzu Corporation)

[0091] Scanning speed: high speed

[0092] Scanning range: 300 to 800 nm

[0093] Temperature and humidity: 23° C. and 50% RH

[0094] The dye coating liquid thus prepared was spin-coated on thesurface of the reflective layer by varying rotational frequency from 300to 4000 rpm at 23° C. and 50% RH to thereby form a recording layer.Then, the coating layer was kept for 1 to 4 hours at 23° C. and 50% RH.Thereafter, a UV-curable adhesive (SD-347 manufactured by Dainippon Inkand Chemicals Inc.) was spin-coated on the recording layer at arotational frequency of 100 to 300 rpm, and the layer was overlaid witha polycarbonate sheet as a cover layer (PUREACE having a thickness of 70μm, manufactured by Teijin Ltd.). The adhesive was then spread over theentire surface by varying rotational frequency from 300 to 4000 rpm.Thereafter, the bonding layer was cured by irradiation by ultravioletlight. In this way, the samples of Examples 1 to 9 were manufactured.

Example 10

[0095] The grooved side of the polycarbonate substrate, which wasobtained by injection molding and which had the same thickness anddiameter as those of the substrates of Examples 1 to 9 and had spiralgrooves (having a depth of 100 nm, a width of 0.11 μm, and a track pitchof 300 nm), was sputtered with Ag so that a reflective layer having athickness of 100 nm was formed. After that, a dielectric layer ofZnS—SiO₂ (having a thickness of 90 nm) was formed by sputtering. Next,20 g of a mixture, which was composed of 95% by mass of FOM-561(phthalocyanine having an absorbance of 0.1, manufactured by Wako PureChemical Industries, Ltd.) and 5% by mass of FOM-559 (phthalocyaninehaving an absorbance of 0.06, manufactured by Wako Pure ChemicalIndustries, Ltd.) was dissolved in 1 L of dibutyl ether by carrying outan ultrasonic treatment for 2 hours to thereby obtain a dye coatingliquid. The dye coating liquid thus prepared was spin-coated on thesurface of the dielectric layer by varying rotational frequency from 300to 4000 rpm at 23° C. and 50% RH. Then, the coated layer was kept for 1hour at 23° C. and 50% RH. Thereafter, a light-transmissive layer ofSiO₂ (having a thickness of 90 nm) was formed by sputtering. Next, aUV-curable adhesive (SD-661 manufactured by Dainippon Ink and ChemicalsInc.) was spin-coated on the layer at a rotational frequency of 100 to300 rpm and the layer was overlaid with a benzotriazole-containingpolycarbonate sheet as a cover layer (PUREACE having a thickness of 80μm, manufactured by Teijin Ltd.). The adhesive was then spread over theentire surface by varying rotational frequency from 300 to 4000 rpm.Thereafter, the bonding layer was cured by ultraviolet pulse irradiationusing an ultraviolet lamp. In this way, a sample was manufactured.

Comparative Example 1

[0096] The grooved side of the polycarbonate substrate, which wasobtained by injection molding and which had the same thickness anddiameter as those of the substrates of Examples 1 to 9 and had spiralgrooves (having a depth of 100 nm, a width of 0.11 μm, and a track pitchof 300 nm), was sputtered with Ag so that a reflective layer having athickness of 100 nm was formed. Next, 20 g of ORASOL BLUE BL (having anabsorbance of 0.06) was dissolved in 1 L of 2,2,3,3-tetrafluoropropanolby carrying out an ultrasonic treatment for 2 hours to thereby obtain adye coating liquid. The dye coating liquid thus prepared was spin-coatedon the surface of the reflective layer by varying rotational frequencyfrom 300 to 4000 rpm at 23° C. and 50% RH to thereby form a recordinglayer. Then, the coated layer was kept for 1 hour at 23° C. and 50% RH.Next, a UV-curable adhesive (SD-347, manufactured by Dainippon Ink andChemicals Inc.) was spin-coated on the layer at a rotational frequencyof 100 to 300 rpm and the layer was overlaid with a polycarbonate sheetas a cover layer (PUREACE having a thickness of 80 μm, manufactured byTeijin Ltd.). The adhesive was then spread over the entire surface byvarying rotational frequency from 300 to 4000 rpm. Thereafter, thebonding layer was cured by ultraviolet pulse irradiation using anultraviolet lamp. In this way, a sample was manufactured.

Comparative Example 2

[0097] The grooved side of the polycarbonate substrate, which wasobtained by injection molding and which had the same thickness anddiameter as those of the substrates of Examples 1 to 9 and had spiralgrooves (having a depth of 100 nm, a width of 0.11 μm, and a track pitchof 300 nm), was sputtered with Ag so that a reflective layer having athickness of 100 nm was formed. Next, 20 g of ORASOL BLUE BL (having anabsorbance of 0.06) was dissolved in 1 L of 2,2,3,3-tetrafluoropropanolby carrying out an ultrasonic treatment for 2 hours to thereby prepare adye coating liquid. The dye coating liquid thus prepared was spin-coatedon the surface of the reflective layer by varying rotational frequencyfrom 300 to 4000 rpm at 23° C. and 50% RH to thereby form a recordinglayer. Then, the coated layer was kept for 1 hour at 23° C. and 50% RH.Next, a UV-curable adhesive (SD-347, manufactured by Dainippon Ink andChemicals Inc.) was spin-coated on the layer at rotational frequency of100 to 300 rpm and the layer was overlaid with a polycarbonate sheet asa cover layer (PUREACE having a thickness of 80 μm, manufactured byTeijin Ltd.). The adhesive was then spread over the entire surface layerby varying rotational frequency from 300 to 4000 rpm. Thereafter, thebonding layer was hardened by ultraviolet pulse irradiation using anultraviolet lamp. In this way, a sample was manufactured.

[0098] Evaluation of Optical Information Recording Media

[0099] The optical information recording media were evaluated byrecording and playing back the media obtained in Examples 1 to 10 andComparative Examples 1 and 2. The evaluation was conducted as follows.

[0100] By using DDU-1000 (manufactured by PULSETECH Corp.) capable ofemitting a laser having a wavelength of 405 nm, 3T-14T signals wererecorded in the above-mentioned optical information recording media andthe overall jitter was measured. The results are shown in Table 1. TABLE1 Groove depth Track pitch Width Jitter nm (nm) (μm) (%) Example 1 30300 0.11 10 Example 2 40 300 0.11 9 Example 3 70 300 0.11 9 Example 4100 300 0.11 8 Example 5 150 300 0.11 9 Example 6 20 300 0.11 10 Example7 100 200 0.08 10 Example 8 100 400 0.23 11 Example 9 100 400 0.27 12Example 10 100 300 0.11 11 Comparative 100 300 0.11 recording Example 1impossible Comparative 100 300 0.11 20 Example 2

[0101] From Table 1, it can be seen that the jitter of Examples 1 to 10was lower than the jitter of Comparative Examples 1 and 2. That is, theuse of a combination of a phthalocyanine having an absorbance of 0.07 ormore and a phthalocyanine having an absorbance of lower than 0.07enables control of decomposition characteristics of dyes to be improvedso that beautiful pits are formed and jitter is lowered.

[0102] Mode 2

Examples 11 to 19

[0103] Grooved sides of spirally grooved polycarbonate substrates, whichwere obtained by injection molding and which each had a thickness of 1.2mm and a diameter of 120 mm and had groove depth, track pitch, and widthaccording to Table 2 (polycarbonate manufactured by Teijin Ltd., tradename: PANLITE AD5503), were sputtered with Ag so that a reflective layerhaving a thickness of 100 nm was formed. Next, 20 g of a mixture, whichwas composed of 95% by mass of ORASOL BLUE GN (phthalocyanine having anabsorbance of 0.07, manufactured by Chiba Specialty Chemical Corp.) and5% by mass of FOM-561 (phthalocyanice having an absorbance of 0.1,manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 1L of 2,2,3,3-tetrafluoropropanol by carrying out an ultrasonic treatmentfor 2 hours to thereby obtain a dye coating liquid.

[0104] The absorbance of ORASOL BLUE GN was obtained by forming a solidfilm thereof (having a thickness of 100 nm) on a flat substrate ofpolycarbonate and measuring the absorbance by the same apparatus andcondition as those employed in Example 1. The absorbance of FOM-561 wasmeasured in a similar way.

[0105] The dye coating liquid thus prepared was spin-coated on thesurface of the reflective layer by varying rotational frequency from 300to 4000 rpm at 23° C. and 50% RH to thereby form a recording layer.Then, the coated layer was kept for 1 hour at 23° C. and 50% RH.Thereafter, a UV-curable adhesive (SD-347 manufactured by Dainippon Inkand Chemicals Inc.) was spin-coated on the recording layer at arotational frequency of 100 to 300 rpm and the layer was overlaid with apolycarbonate sheet as a cover layer (PUREACE having a thickness of 70μm, manufactured by Teijin Ltd.). The adhesive was then spread over theentire surface by varying rotational frequency from 300 to 4000 rpm.Thereafter, the bonding layer was cured by ultraviolet light irradiationusing an ultraviolet lamp. In this way, a sample was manufactured.

Comparative Example 3

[0106] The grooved side of the polycarbonate substrate (polycarbonatemanufactured by Teijin Ltd., trade name: PANLITE AD5503), which wasobtained by injection molding and which had the same thickness anddiameter as those of the substrates of Examples 11 to 19 and had spiralgrooves (having a depth of 100 nm, a width of 0.11 μm, and a track pitchof 300 nm), was sputtered with Ag so that a reflective layer having athickness of 100 nm was formed. Next, 20 g of ORASOL BLUE GN (having anabsorbance of 0.07) was dissolved in 1 L of 2,2,3,3-tetrafluoropropanolby carrying out ultrasonic treatment for 2 hours to thereby obtain a dyecoating liquid. The dye coating liquid thus prepared was spin-coated onthe layer by varying rotational frequency from 300 to 4000 rpm at 23° C.and 50% RH. Then, the coating layer was kept for 1 hour at 23° C. and50% RH. Next, a UV-curable adhesive (SD-347 manufactured by DainipponInk and Chemicals Inc.) was spin-coated on the layer at a rotationalfrequency of 100 to 300 rpm and the layer was overlaid with apolycarbonate sheet (PUREACE having a thickness of 80 μm, manufacturedby Teijin Ltd.). The adhesive was then spread over the entire surface byvarying rotational frequency from 300 to 4000 rpm. Thereafter, thebonding layer was cured by ultraviolet pulse irradiation using anultraviolet lamp. In this way, a sample was manufactured.

Comparative Example 4

[0107] The grooved side of the polycarbonate substrate, which wasobtained by injection molding and which had the same thickness anddiameter as those of the substrates of Examples 11 to 19 and had spiralgrooves (having a depth of 100 nm, a width of 0.11 μm, and a track pitchof 300 nm), was sputtered with Ag so that a reflective layer having athickness of 100 nm was formed. Next, 20 g of FOM-561 (having anabsorbance of 0.1) was dissolved in 1 L of 2,2,3,3-tetrafluoropropanolby carrying out ultrasonic treatment for 2 hours to thereby obtain a dyecoating liquid. The dye coating liquid thus prepared was spin-coated onthe layer by varying rotational frequency from 300 to 4000 rpm at 23° C.and 50% RH. Then, the coated layer was kept for 1 hour at 23° C. and 50%RH. Next, a UV-curable adhesive (SD-347 manufactured by Dainippon Inkand Chemicals Inc.) was spin-coated on the layer at a rotationalfrequency of 100 to 300 rpm and the layer was overlaid with apolycarbonate sheet (PUREACE having a thickness of 80 μm, manufacturedby Teijin Ltd.). The adhesive was then spread over the entire surface byvarying rotational frequency from 300 to 4000 rpm. Thereafter, thebonding layer was cured by ultraviolet pulse irradiation using anultraviolet lamp. In this way, a sample was manufactured.

[0108] Evaluation of Optical Information Recording Media

[0109] The optical information recording media were evaluated byrecording and playing back the media obtained in Examples 11 to 19 andComparative Examples 3 and 4. The evaluation was conducted as follows.

[0110] By using DDU1000 (manufactured by PULSETECH Corp.) capable ofemitting a laser having a wavelength of 405 nm, 3T-14T signals wererecorded by a recording power of 5 mW in the above-mentioned opticalinformation recording media and the overall degree of modulation andreflectance were measured. The results are shown in Table 2. TABLE 2Groove Track Degree of depth pitch Width modulation Reflectance (nm)(nm) (μm) (%) (%) Example 11 30 300 0.11 42 52 Example 12 40 300 0.11 4954 Example 13 70 300 0.11 51 59 Example 14 100 300 0.11 48 62 Example 15150 300 0.11 45 60 Example 16 160 300 0.11 40 58 Example 17 100 200 0.0847 57 Example 18 100 500 0.23 46 55 Example 19 100 600 0.22 44 50Comparative 100 300 0.11 35 55 Example 3 Comparative 100 300 0.11 30 15Example 4

[0111] As can be seen from Table 2, Examples 11 to 19 exhibit a higherdegree of modulation relative to Comparative Examples 3 and 4. That is,the use of a combination of two or more organic solvent-solublecompounds each having an absorbance of 0.07 or more at the recordinglaser wavelength enables satisfactory control of the accumulation ofheat by laser and enhancement of degree of modulation.

[0112] It can also be seen that controlling absorbance makes it possibleto maintain a high reflectance.

[0113] Accordingly, information can be recorded on the opticalinformation recording medium of the invention by irradiating the mediumwith even a short-wave laser having a wavelength of 600 nm or less.Moreover, the optical information recording medium of the inventionexhibits stable recording and playback characteristics.

What is claimed is:
 1. An optical information recording mediumcomprising a substrate including a groove that has a track pitch of 200to 400 nm and a depth of 20 to 150 nm, the substrate having successivelydisposed thereon a light-reflective layer, a recording layer containinga dye and on which information is recordable by a laser beam having awavelength of 600 nm or less, and a cover layer, wherein the recordinglayer contains at least one organic solvent-soluble compound having anabsorption maximum in the range of 300 to 450 nm and an absorbance of0.07 or more at a recording laser wavelength, and at least one organicsolvent-soluble compound having an absorption maximum in the range of300 to 450 nm and an absorbance of lower than 0.07 at a recording laserwavelength.
 2. The optical information recording medium according toclaim 1, wherein the at least one organic solvent-soluble compoundhaving the absorbance of 0.07 or more at a recording laser wavelength isa phthalocyanine compound, and the at least one organic solvent-solublecompound having the absorbance of lower than 0.07 at a recording laserwavelength is a phthalocyanine compound or an anthracene compound. 3.The optical information recording medium according to claim 1, whereinthe phthalocyanine compound is at least one of a sulfamoyl-substitutedphthalocyanine compound, an alkyl-substituted phthalocyanine compound,and an alkoxy-substituted phthalocyanine compound.
 4. The opticalinformation recording medium according to claim 1, wherein the organicsolvent-soluble compound having the absorbance of 0.07 or more at arecording laser wavelength is included in the recording layer at 5 to95% by mass.
 5. The optical information recording medium according toclaim 1, wherein the organic solvent-soluble compound having theabsorbance of 0.07 or more at a recording laser wavelength is includedin the recording layer at 10 to 90% by mass.
 6. The optical informationrecording medium according to claim 1, wherein the dye is at least oneselected from the group consisting of a triazole compound, a triazinecompound, a cyanine compound, a merocyanine compound, an aminobutadienecompound, a phthalocyanine compound, a cinnamic acid compound, aviologen compound, an azo compound, an oxonolbenzoxazole compound and abenzotriazole compound.
 7. The optical information recording mediumaccording to claim 1, wherein the light-reflective layer contains alight-reflective substance selected from the group consisting of Cr, Ni,Pt, Cu, Ag, Au, Al and stainless steel.
 8. The optical informationrecording medium according to claim 1, wherein the recording layercontains an anti-fading agent.
 9. The optical information recordingmedium according to claim 8, wherein the anti-fading agent is a singletoxygen quencher.
 10. The optical information recording medium accordingto claim 1, wherein a bonding layer is disposed between the recordinglayer and the cover layer.
 11. The optical information recording mediumaccording to claim 1, wherein a dielectric layer or a light-transmissivelayer is disposed between the light-reflective layer and the recordinglayer.
 12. The optical information recording medium according to claim11, wherein the dielectric layer contains an oxide, a nitride, acarbide, or a sulfide of any one of Zn, Si, Ti, Te, Sm, Mo and Ge. 13.The optical information recording medium according to claim 1, whereinthe recording laser wavelength is 405 nm.
 14. An optical informationrecording medium comprising a substrate including a groove that has atrack pitch of 200 to 400 nm and a depth of 20 to 150 nm, the substratehaving successively disposed thereon a light-reflective layer, arecording layer containing a dye and on which information is recordableby a laser beam having a wavelength of 600 nm or less, and a coverlayer, wherein the recording layer contains at least two organicsolvent-soluble compounds, each having an absorption maximum in therange of 300 to 450 nm and an absorbance of 0.07 or more at a recordinglaser wavelength.
 15. The optical information recording medium accordingto claim 14, wherein the organic solvent-soluble compound having theabsorbance of 0.07 or more at a recording laser wavelength is selectedfrom the group consisting of a phthalocyanine compound, a porphyrincompound, a triazole compound, an aminobutadiene compound and a cyaninecompound.
 16. The optical information recording medium according toclaim 15, wherein the phthalocyanine compound is at least one of analkoxy-substituted phthalocyanine compound, a sulfonamide-substitutedphthalocyanine compound, a sulfamoyl-substituted phthalocyanine compoundand a sulfonic acid-substituted phthalocyanine compound.
 17. The opticalinformation recording medium according to claim 14, wherein the organicsolvent-soluble compound having the absorbance of 0.07 or more at arecording laser wavelength is included in the recording layer at 50 to100% by mass.
 18. The optical information recording medium according toclaim 14, wherein the light-reflective layer contains a light-reflectivesubstance selected from the group consisting of Cr, Ni, Pt, Cu, Ag, Au,Al and stainless steel.
 19. The optical information recording mediumaccording to claim 14, wherein a dielectric layer or alight-transmissive layer is disposed between the light-reflective layerand the recording layer.
 20. The optical information recording mediumaccording to claim 14, wherein the recording laser wavelength is 405 nm.